The critical t-statistic can be found from either the Calc menu tools under Probability Distributions, or from the Graph menu and Probability Distribution Plot…. Here, we will find the critical t-statistic using the graphical tools used in probability distribution plots. In this recipe, we will find the critical t-statistic with 14 degrees of freedom for a two-sided test.
The following steps will show us how we can use the probability distribution plot tools to find the critical t-statistic:
14
.0.05
.Probability distribution plots allow us to easily create a graph of a distribution curve based on the parameters entered. Using the option to view probability, we will generate a distribution curve with a shaded area under the curve.
The previous steps created the t-distribution curve and shaded the area below 0.025 and above 0.975. Overall, 5 percent of the curve is shaded and the position of the 0.025 and 0.975 in T is displayed. This is our critical t-statistic for a t-test, as shown in the following screenshot:
From the graph, the critical t for a two-sided test with df equal to 14 is 2.145.
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